Disk clutches or disk brakes usually comprise a plurality of annular disks. A first group with toothed outside disks is arranged rotationally fixed in a disk carrier, and a second group with toothed inside disks is arranged rotationally fixed on a hub. Viewed in the axial direction of the shift element, the disks of the two groups engage in one another in the manner of gears. The two groups can be displaced, relative to one another, in the axial direction and can, therefore, be brought into frictional connection in pairs.
Friction lining plates are usually constructed as sandwiches with a support sheet consisting, for example, of steel, and with at least one friction lining arranged on an annular surface of the support sheet and generally fixed permanently to the latter. The friction lining generally consists of a fibrous mass made from a paper-containing material or even of carbon.
In practice, disks covered by a friction lining on one side and also on both sides are used. In the case of disks lined on one side, in each case, two adjacent disks co-operate in the sense that the friction lining of one disk comes in contact with the support sheet of the other disk when the shift element is engaged. With disks lined on both sides, in each case, a disk lined on both sides is arranged between two adjacent unlined disks. These smooth, unlined disks are usually made of steel.
As is known, during a shift process and, especially during prolonged slip operation of such a disk clutch or disk brake in friction surface contact, high temperatures are produced owing to the friction work and friction power involved. To dissipate the corresponding large amount of heat outwards, a flow of suitable coolant and lubricant—generally oil—onto the disks is usually provided. In most cases, the stream of cooling oil passes over the disks radially outward from their inside diameter and flows through the disk pack through grooves milled or pressed into the friction lining, generally from the inside outward.
To improve the heat dissipation, numerous geometrical designs are known for friction lining grooves. As basic groove patterns, groups of parallel grooves, so-termed waffle grooves, radial grooves and tangential grooves can be mentioned. Frequently, different basic groove patterns are combined with one another.
For example, from U.S. Pat. No. 5,335,765, a wet-running, friction lining plate for an automatic transmission clutch is known, in which two sets of grooves are pressed into the friction surface. The grooves of the two groove sets are distributed symmetrically on the circumference of the friction surface. Each groove of the two groove sets extends at an oblique angle inclined backward relative to the rotation direction from the inside edge of the friction surface to its outer edge. The cooling oil for heat dissipation passes from the inside diameter of the friction surface into the grooves. To achieve a rapid flow of cooling oil from the inside outward, the inclination angle of the grooves of the second groove set is larger than the inclination angle of the grooves of the first groove set, such that each of the second grooves opens into a first groove and extends from that point outward to the outer diameter of the friction surface. The first and second grooves “meet” near the inside diameter of the friction surface, such that the cooling oil inlet cross-section available for cooling oil to flow radially through the friction lining plate, corresponds to the free cross-section of the first grooves at the inside diameter of the friction surface. The cooling oil outlet cross-section corresponds to the sum of the free cross-sections of the first and second grooves at the outer diameter of the friction surface and is about twice as large as the cooling oil inlet cross-section. In relation to the area of the friction lining, the total grooved fraction is relatively small. Corresponding to the orientation of the two groove sets, this friction lining plate has a preferred rotation direction and can only be operated in this one rotation direction without adverse effect on its function.
For the converter-bridging clutch of a torque converter, DE 44 32 624 C1 proposes a friction lining attached on an axially displaceable piston, which has a plurality of grooves or recesses for the passage of cooling oil that extend between the radially outer and radially inner edge of the friction lining in the circumferential direction at a defined angle with a varying radial distance from the rotation axis of the friction lining. Each groove or recess changes its extension direction between an inlet and an outlet point for the cooling oil at least once so that its radial component is directed the opposite way to that before the change. Distributed circumferentially there are only a few inlets at the outside diameter of the friction lining and only a few outlets at its inside diameter. The inlets and outlets of the grooves are perpendicular to the rotation direction. Along the course of each groove from the radially outer to the radially inner edge of the friction lining pockets are arranged in the groove cross-section for the intermediate storage of cooling oil. Correspondingly, the groove cross-section expands in sections along the course of the groove and then narrows again further along. The inlet and outlet cross-sections of individual grooves are the same. This groove design is intended to give the most uniform possible cooling of the friction lining surface without needing a comparatively large cooling oil throughput for this.
Besides the cooling oil throughput through the disk pack of the frictional shift element in a shifting process and during prolonged slip operation, the geometrical design of the friction lining grooves also influences the rotary vibration behavior of the frictional shift element when torque is taken up in the shifting process. Regardless of the rotation uniformity of the input torque of the frictional shift element, an unfavorable variation of the coefficient of friction acting between the contact areas of the disks can lead to self-induced, irritating rotary vibrations. Such an unfavorable friction coefficient variation can, for example, come about if a “planing effect” that depends on a rotation speed difference occurs between the smooth disk surfaces and the friction lining surfaces when disks lined on both sides with a friction lining are used, i.e., between steel and lining disk surfaces. This effect is known in practice, especially with disk clutches or disk brakes, with a high torque capacity and high cooling oil demand because of the frictional work.
To compensate such “planing effects”, DE 199 57 511 A1 proposes a friction lining plate for a shift clutch in which the two different basic groove, shape patterns are combined with one another. On the one hand, the friction lining fixed on the annular support sheet has several grooves distributed at the circumference, which run from the inside diameter of the friction lining along radial lines or secants and are cut relatively deeply (if necessary, down to the support sheet) in the friction lining. These grooves serve as “pumping grooves” for the cooling oil passing outward from the inside diameter of the friction lining and they convey relatively large oil flows and thus carry away a large part of the friction heat generated during slipping operation. In addition, the friction lining has a second group of grooves arranged on the surface of the friction lining in the manner of a grid and cut less deeply into the friction lining. Thus, this “waffle grooving” overlaps with the groove pattern of the “pumping grooves” and is mainly intended to reduce excess cooling oil and, therefore, also hydrodynamic effects which result in “planing” of the friction linings on the oil film. Correspondingly, the grooves of the “waffle grooving” are more numerous than the “pumping grooves” and are also much closer together so that individual “waffle grooves” can always be associated with one of two subgroups. The grooves of these two subgroups run parallel to one another and the grooves of the two subgroups intersect at a certain angle (preferably 90 degrees). In accordance with the non circular-symmetric orientation of the “waffle grooving”, the free groove cross-section of individual “waffle grooves” at the inside diameter of the friction lining, into which the cooling oil supplied can enter directly, is rather random. In production technology terms, the “waffle grooving” is superimposed on the “pumping grooves” and the production of such a friction lining plate is a correspondingly elaborate and costly process.
The purpose of the present invention is to develop a friction lining plate for a wet-running, frictional shift element which, on the one hand, enables the dissipation of a large amount of heat produced during slippage and, on the other hand, is not sensitive to rotary vibrations when the torque is taken up as the frictional shift element closes. The friction, lining plate must also be usable independently of the rotation direction without adverse effect on its function and should be comparatively inexpensive to manufacture.